The emergence of the Asynchronous Transfer Mode (ATM) networking protocol is a response to the demand for faster data communications and more sophisticated processing. The ATM protocol relates to a cell-based switching and multiplexing, technology and is designed to be a general purpose transfer mode for a wide range of traffic services. Communications networks now serve a range of new applications involving mixed media traffic comprising data, voice, still and moving images and video. ATM is a technology designed for flexibility to enable the carriage of multiple and previously segregated traffic over a single, common backbone infrastructure. The aim of the ATM networking protocol is to provide a more flexible facility for the transmission of such traffic and for the allocation of transmission bandwidth in order to efficiently utilize network resources.
Another goal of ATM network design is to provide a backbone network capable of accommodating differentiated services in a scalable manner. In order to maximize the efficiency of an ATM network, network designers provision ATM networks in which a consolidated backbone network is shared among differentiated services. Yet other goals of network design are to maximize utilization of provisioned links, maximize statistical gains and reduce network management complexity.
The ATM networking protocol is particularly advantageous in that it provides network administrators and end users with multiple classes of communications service in order to accommodate the various service requirements of different applications. The ATM Forum Traffic Management Working Group has defined five service categories for cell transmission, also referred to herein as classes of transmission service, which are distinguished by parameter sets used to describe source behaviour and quality of service (QoS) guarantees. These service categories are identified as constant bit rate (CBR), real time variable bit rate (rtVBR), non-real time variable bit rate (nrtVBR), available bit rate (ABR) and unspecified bit rate (UBR), all of which are set out in the “ATM Forum Traffic Management Specification”, Version 4.0, which was published by the ATM Forum Technical Committee under document no. af-tm-0056.000 in April 1996 (“the Traffic Management Specification”). The above five service categories can be grouped more generally into real time and non-real time service categories, with CBR and rt-VBR constituting the real time group and nrt-VBR, ABR and UBR constituting the non-real time group. While other service categories may be proposed or adopted over time, these can likewise be expected to be differentiated into real time and non-real time groups.
The ABR and UBR service categories of ATM networking are intended to carry data traffic which has no specific cell loss or delay guarantees. The UBR service category is the simplest of the two, as it optionally provides only a guaranteed minimum cell rate. The ABR service category provides source to destination flow control that attempts, but is not guaranteed, to achieve zero cell loss. Thus, the ABR service category offers users a relatively high quality of service in terms of cell loss probability and yet seeks to maintain high network resource utilization. Traffic management techniques such as those adopting flow control are used to protect a network and its various end-systems from congestion in order to achieve network performance and utilization objectives.
ATM cell traffic between nodes in an ATM network is carried on what are known as virtual connections (VC). Traffic from end user to end user through a plurality of intermediate nodes is carried on Virtual Channel Connections (VCC). VCCs may carry different categories of traffic (eg. voice, video, data) which are required to be transmitted with specific service guarantees. Often, VCCs having different sources and different destinations will nevertheless share network resources for portions of their respective connections. This is particularly true in the backbone or core of a network in which traffic from many sources is merged onto higher capacity connections. In the prior art, where several VCCs share portions of a network, it has been known to combine VCCs which have identical quality of service (QoS) requirements onto Virtual Path Connections (VPC) in order to simplify the processing of traffic on these portions of the network. When different VCCs do not share the same ultimate destination, it is necessary to reconstitute the VCCs at the termination point or destination of the VPC. One of the objectives of combining VCCs having identical QoS requirements onto VPCs is to enable the nodes in the VPC to handle the traffic in a manner such that the VCCs are transparent, i.e., ATM cells on a VPC are processed essentially without regard to the VCC with which they are associated. The aggregation of VCCs onto VPCs reduces network management complexity and can increase utilization of provisioned links.
Because the component VCCs of a prior art backbone VPC have identical quality of service requirements, it is not necessary to perform traffic management functions in the VPC at the VCC level. That is, all traffic in the VPC may be treated identically without regard to the VCC. This simplification is generally believed to allow for faster and more efficient transmission of the traffic since traffic management functions may be performed at the VPC level. Thus, where several VPCs are being carried over a physical link in a network, arbitration may be performed between the VPCs instead of the VCCs. Since there will be fewer VPCs than VCCs, the traffic management function is simplified. As well, since the use of backbone VPCs requires that all traffic in a single VPC be treated in the same manner, it is usual to combine VCCs of a given category of service onto dedicated VPCs which provide the appropriate service guarantees identically corresponding to the underlying VCC traffic.
Where VCCs having many different level of service requirements are present, in the prior art multiple VPCs are provided in order to furnish those levels of service to the VCCs. For instance, in the prior art networks it is necessary to provide more than one non-real time VPC in order to accommodate the different levels of service required by the various categories of non-real time connections. Some non-real time connections may need a guarantee of a minimum transmission rate, while others may not require any transmission rate guarantees and may be serviced on a best effort basis only. Separate VPCs are therefore provisioned in prior art networks in order to accommodate these varying service requirements. It will be appreciated that the provisioning of VPCs having multiple classes of service in the core or backbone of an ATM network tends to increase the complexity of the traffic management functions performed by the nodes therein.
There is therefore a need in a connection oriented network to provide a method for combining many non-real time connections having various levels of service requirements onto a single path such that the traffic on the path may be managed without regard to the particular level of service of each connection. There is also a need to establish connections and paths in a connection oriented network according to a method which allows for a high degree of network resource utilization but still ensures that the various levels of service associated with the connections are met.